U.S. dishes from six chains (Burger King, Domino's, Kentucky Fried Chicken, McDonald's, Pizza Hut and Subway) generally contained more salt (both per overall serving and per 100 grams of food) than the same menu items in Australia, France, New Zealand and the U.K.

Neck and neck with the U.S., however, was Canada. One of the widest disparities in salt content was found between different countries' chicken nuggets. A serving of McDonald's nuggets in the U.K. packs 0.6 grams of salt, or 240 milligrams of sodium. In the U.S., the amount jumps to 1.5 grams (600 mg); in canada it leaps to 1.7 grams (680 mg).

According to the University of Calgary's Norman Campbell — who worked on the study and is an active member of the World Action on Salt and Health — it's unclear why these variations in salt levels exist, though it's possible that they're linked to the U.K. government's decision to set voluntary salt-reduction "targets" for the packaged food industry.

McDonald's, for one, seem up to the task. "We have already reduced sodium by 10 percent in the majority of our national chicken menu offerings in the U.S. — most recently Chicken McNuggets — a Happy Meal favorite," a spokesperson told Reuters. "Sodium reductions will continue across the menu and by 2015, we will reduce sodium an average of 15 percent across our national menu of food choices."